Group III-V compound semiconductors such as, for example, GaN and AlGaN are widely used for optoelectronics and electronics because of many advantages such as, for example, easily controllable wide band gap energy.
In particular, light emitting devices, such as light emitting diodes or laser diodes, which use group III-V or II-VI compound semiconductors, are capable of emitting visible and ultraviolet light of various colors such as red, green, and blue owing to development of device materials and thin film growth techniques. These light emitting devices are also capable of emitting white light with high luminous efficacy through use of a fluorescent substance or color combination and have several advantages of low power consumption, semi-permanent lifespan, fast response speed, safety, and environmental friendliness as compared to conventional light sources such as, for example, fluorescent lamps and incandescent lamps.
Accordingly, application sectors of the light emitting devices are expanded up to transmission modules of optical communication means, light emitting diode backlights to replace Cold Cathode Fluorescence Lamps (CCFLs) which serve as backlights of Liquid Crystal Display (LCD) apparatuses, white light emitting diode lighting apparatus to replace fluorescent lamps or incandescent lamps, vehicular headlamps, and traffic lights.
In a light emitting device, a light emitting structure, which includes an undoped semiconductor layer (un-GaN layer), a first conductive semiconductor layer (n-GaN layer), an active layer (MQW layer), and a second conductive semiconductor layer (p-GaN layer), may be formed on a substrate formed of, for example, sapphire, and a first electrode and a second electrode may be disposed respectively on the first conductive semiconductor layer and the second conductive semiconductor layer.
The light emitting device is configured to emit light having energy determined by the inherent energy band of a constituent material of the active layer in which electrons injected through the first conductive semiconductor layer and holes injected through the second conductive semiconductor layer meet each other. The light emitted from the active layer may vary based on the composition of the constituent material of the active layer, and may be, for example, blue light, ultraviolet (UV) light, deep UV light, or light of various other wavelength ranges.
Light in a first wavelength range emitted from the light emitting device may excite phosphors, and light in a second wavelength range may be emitted from the phosphors. The phosphors may be included in a molding part surrounding the light emitting device, or may be disposed in the form of a phosphor film.
FIG. 1 is a sectional view illustrating a light emitting device package, and FIG. 2 is a top view illustrating a light emitting device illustrated in FIG. 1.
The light emitting device package 100 includes a body 110 having a cavity, a first lead frame 121 and a second lead frame 122 installed to the body 110, a light emitting device 130 installed to the body 110 and electrically connected to the first lead frame 121 and the second lead frame 122, and a molding part 160 formed in the cavity.
The light emitting device 130 may be directly electrically connected to the first lead frame 121, and a first electrode pad 140 on the light emitting device 130 may be bonded to the second lead frame 122 via a wire 150. The molding part 160 may include phosphors 165.
A portion of the body 110, which serves as a reflective surface R at the lateral side of the cavity, may configure a slope. When the light emitting device 130 is disposed at the center of the bottom surface of the cavity, the reflective surface R of the cavity may have a left-right symmetrical shape.
However, the conventional light emitting device has the following problem.
Since at least one first electrode pad 140 is disposed on the top of the light emitting device 130, the area in which the first electrode pad 140 is disposed may suffer from a reduction in the flux of light because light emitted from the interior of the light emitting device 130 is reflected by the first electrode pad 140.
That is, referring to FIGS. 2(a) and (b), the flux of light at the right area, provided with the pad 140, may be smaller than the flux of light at the left area. As the development of micro-processing technologies leads to a reduction in the size of a cavity structure, the flux of light emitted from the light emitting device package 100 may exhibit uneven distribution according to the arrangement of the first electrode pad 140 on the light emitting device 130. More specifically, since the flux of light emitted from the top of the right area of the light emitting device 130 is small, the reflection of the reflective surface R may cause the smaller flux of light to propagate leftward, outside of the light emitting device package 100.